Advanced Power Electronics and Smart Inverters

Integrating renewable and distributed energy resources, such as photovoltaics (PV)
and energy storage devices, into the electric distribution system requires advanced
power electronics, or smart inverters, that provide grid services such as voltage
and frequency regulation, ride-through, dynamic current injection, and anti-islanding
functionality.

NREL researchers are engaged in a spectrum of smart inverter research that includes
designing novel wide-bandgap smart inverters, developing robust control algorithms
for better inverter functionality, determining interactions between multiple smart
inverters and between inverters and utility distribution systems, supporting standards
development for smart inverter functionalities, and analyzing the impacts of smart
inverters on distribution systems. These activities are focused on enabling high penetrations
of renewable and distributed energy resources on the U.S. electricity grid to make
it cleaner, reliable, and more efficient.

Capabilities

Modeling and simulation of smart inverters

Design of smart inverter hardware and firmware

Development of smart inverter control algorithms

Development of wide-bandgap smart inverters

Use of control and power hardware-in-the-loop techniques to determine interactions
between multiple inverters at multiple points of common coupling

Development and validation of test procedures for smart inverters to support IEEE
1547 and UL 1741

Power system impact studies for smart inverter-interfaced distributed energy resources

Projects

To enable the integration of hundreds of gigawatts of solar generation into the U.S.
electric power system, NREL is designing a PV inverter that combines high-voltage
silicon carbide with revolutionary concepts such as additive manufacturing and multi-objective
magnetic design optimization to achieve better performance and reliability at lower
cost. This project includes a high-voltage silicon carbide-based power block, advanced
gate driver, flexible controller board, advanced grid-support control algorithms,
communications interface for interoperability, multi-objective magnetic design tools,
high-power-density inverter design, prototyping, and grid integration testing of the
new inverter.

Advanced Energy Industries validated its advanced PV inverter technology using NREL's power hardware-in-the-loop
system and megawatt-scale grid simulators. Our utility-scale power hardware-in-the-loop
capability allowed Advanced Energy to loop its inverter into a real-world simulation
environment so researchers could see the impact of the inverter's advanced features
on power reliability and quality. Advanced Energy's inverter will help support a smarter
grid that can handle two-way flow of power and communication while reducing hardware
costs.

Florida Power and Light commissioned a 1.1-MW AC PV solar canopy that shades parking
spaces at the Daytona Motor Speedway in Daytona Beach, Florida. In addition to generating
clean solar electricity, the site serves as a test platform for solar inverters. Thirty-six
grid-connected inverters from eight inverter manufacturers are installed on site,
allowing Florida Power and Light to gain insight into the products' efficiency, grid
support performance, reliability, and cost.

Florida Power and Light partnered with NREL to provide performance evaluations of
several of the inverter types installed at this site. In the Energy Systems Integration Facility, NREL researchers are able to test the inverters under a range of operating conditions
in a controlled laboratory environment. Nine types of tests were run in this study:
voltage ride-through, frequency ride-through, fixed power factor operation, frequency-watt
control, volt/VAR control, efficiency, anti-islanding, load rejection overvoltage,
and single- and three-phase faults.

Reaching Department of Energy goals of 20% wind energy by 2030 and 35% by 2050 requires
a better understanding of power system reliability at high levels of wind energy penetration.
These important questions need to be addressed to enable high-penetration scenarios:

What is the role for short-term power storage to provide power variability smoothing
for wind turbine drivetrain loads?

Can system stability and reliability be maintained with high instantaneous wind penetrations?

What is the role of energy storage to firm wind power ability to provide such controls?

How can other enabling technologies, such as response loads, help integrate high levels
of variable power?

What testing needs to be done to enable this transformation?

The goal of this project is to develop and test coordinated controls of active power
by wind generation, short-term energy storage, and large industrial motor drives to
provide ancillary services to the grid and minimize loading impacts, thereby reducing
operation and maintenance costs and the cost of energy generated by wind power.

NREL is collaborating with SolarCity to address the safety, reliability, and stability challenges of interconnecting high
penetrations of distributed PV with the electric power system. This work includes
collaborating with the Hawaiian Electric Companies to analyze high-penetration solar scenarios using advanced modeling and inverter
testing.

NREL partnered with Solectria to develop PV inverters with advanced features that can support the electric grid.
To get more solar power onto the grid, researchers are working to find ways to tame
solar power's variable nature. Solar inverters offer the potential to help with this,
and manufacturers such as Solectria are developing advanced inverters that can better
manage solar power reliability and quality.